This topic made me think...for the past 24 years..I have driven Ram 1500's...(a new one every 3 years) I log 120,000 plus miles on each one...I have never had a brake fluid flush service on any of them...they are work trucks...(severe duty)...never had an issue...now my cars are in a controlled environment 50% humidity...65 degree temp all year long...I have never had a brake flush service on any of them....again never a problem....yet my bikes have a complete dealer service EVERY 2 yrs....(with the brake fluid flush)....what does all this mean

....I have no idea...I'm not that smart..
Keeping them for the first 3 years, you're not seeing the affects of moisture in the lines/calipers, and frankly what you're describing sounds fine.
If you were at the end of 20years, which people do ALL of the time, you would see rust inside the caliper pistons, and notably degraded braking because all of the water content in your fluid boils quickly compared to brake fluid.
BUT, if you're driving a truck, like a truck, in the city, no hills, no heat in the brakes, no weight, no stress, you could probably run peanut butter and not really know the difference.
If you took that 20year old truck and stressed the brakes, you'd find out in a big hurry about water contaminated fluid, or come out here and come down I-70 from the Continental Divide into Denver, and boil, and then fade them...
...happens all of the time, occasionally even makes the local news... ...occasionally...